Between 2003 and 2005 Hafsås competed in international junior races. Several times he achieved good results in the Junior European Cup, including a second place in Geilo's sprint . At the Biathlon Junior World Championships 2003 in Haute-Maurienne , he won the gold medal with the relay. At the Junior Ski World Championships in 2004 in Stryn , Norway , he was tenth over ten kilometers in the free technique and fifth with the Norwegian relay. At the Junior Ski World Championships in 2005 in Rovaniemi , Finland , he barely missed precious metal as fourth over ten kilometers in the free Tedchnik. In the 2007/08 season Hafsås was first used in the European Biathlon Cup , where he scored two victories with the individual in Langdorf and the relay race in Osrblie . In February 2008 Hafsås made his debut in Pyeongchang in the Biathlon World Cup . After a 41st place for his debut in the sprint, he improved to 21st place in the pursuit and won his first World Cup points. In the same season he came in ninth in a sprint in Khanty-Mansiysk for the first time in the top ten. In the first sprint of the 2008/09 season in Östersund , the Norwegian came in sixth. In addition, Hafsås succeeded in Lygna in December 2008 over 30 km freestyle a victory in the Nordic Scandinavian Cup .
Hafsås achieved his first victory in a World Cup competition at the start of the 2009/10 Cross-Country World Cup . In Beitostølen he won the 15 km free technique competition with 0.2 seconds ahead of Vincent Vittoz . Just one day later, Hafsås was able to celebrate his second World Cup victory with the Norwegian relay.
After the Biathlon World Cup in Pokljuka, Hafsås decided not to contest any more biathlon competitions in the 2009/10 season and instead to concentrate on cross-country skiing. At the 2010 Winter Olympics , however, he was only 42nd in the 15-kilometer race in free technique. Hafsås then started again at the Biathlon World Cup in Kontiolahti. But he was last used in the cross-country skiing world cup in November 2011 in Sjusjøen when he was 38th. In January 2012, Hafsås won his third race in the IBU Cup at the sprint in Haute Maurienne.
Hafsås' brother Eirik was also a member of the Norwegian national team for several years, but could not celebrate any major successes in the European Cup until his resignation.
Biathlon World Cup placements
The table shows all placements (depending on the year, including the Olympic Games and World Championships).
1st - 3rd Place: Number of podium placements
Top 10: Number of placements in the top ten (including podium)
Points ranks: Number of placements within the point ranks (including podium and top 10)
Starts: Number of races run in the respective discipline